Closed loop aperture tunable antenna

ABSTRACT

An apparatus comprises a radio frequency (RF) antenna circuit; an antenna aperture tuning circuit; an antenna impedance measurement circuit; and a processor circuit electrically coupled to the tunable antenna aperture circuit and the impedance measurement circuit. The processor circuit is configured to: set the antenna aperture tuning circuit to an antenna aperture tuning state according to one or more parameters of an RF communication network; initiate an antenna impedance measurement; and change the antenna aperture tuning state to an antenna aperture tuning state indicated by the antenna impedance.

BACKGROUND

Radio access networks are used for delivering data, voice and videocommunications to devices such as cellular telephones, smart phones,tablet computers, etc. These devices are often included within metalliccases, which creates a challenge to design an antenna for the devicesthat provides the capability desired by users of the devices. Themetallic cases can act as a shield that prevents electromagnetic energyfrom reaching the antenna. Thus, there are general needs for devices,systems and methods that provide robust communication in radio accessdevices that provides a satisfactory experience for the user.

SUMMARY

Embodiments pertain to portable electronic devices that communicateusing radio access networks. These devices are increasingly beingdesigned with metallic cases. However, metallic cases for such devicescan create challenges for antenna design. The more the device is encasedin metal, the more difficult it is to provide enough volume for aneffective antenna design. Additionally, changes in orientation of thedevices by a user and the way a user interacts with the devices(sometimes called “use cases”) further complicate antenna design.

The present subject matter provides an aperture tunable antenna toaddress these issues. To tune the antenna aperture an antenna aperturetuning circuit is provided. The antenna aperture tuning circuit mayinclude or more RF switches. The RF switches can be coupled between aradiating element of the antenna and a circuit component, such as one ormore of an inductor, capacitor, another radiating element of theantenna, and circuit ground for example. The antenna aperture tuningstate can be changed by changing the configuration of the RF switches.

In some embodiments, antenna impedance is obtained and it is determinedif the current antenna aperture tuning state is the desired or optimumtuning state for that impedance. If not, the device changes its antennatuning state accordingly. This creates closed loop control of theantenna aperture tuning state based on antenna impedance.

An apparatus embodiment includes a radio frequency (RF) antenna circuit;an antenna aperture tuning circuit; an antenna impedance measurementcircuit; and a processor circuit electrically coupled to the tunableantenna aperture circuit and the impedance measurement circuit. Theprocessor circuit is configured to: set the antenna aperture tuningcircuit to an antenna aperture tuning state according to one or moreparameters of an RF communication network; initiate an antenna impedancemeasurement; and change the antenna aperture tuning state to an antennaaperture tuning state as a function of the antenna impedance.

A method embodiment includes setting an antenna aperture tuning stateaccording to one or more parameters of the RF communication network;determining antenna impedance; and changing the antenna aperture tuningstate to an antenna aperture tuning state indicated by the determinedantenna impedance.

This section is intended to provide a brief overview of subject matterof the present patent application. It is not intended to provide anexclusive or exhaustive explanation of the invention. The detaileddescription is included to provide further information about the presentpatent application such as a discussion of the dependent clams and theinterrelation of the dependent and independent claims in addition to thestatements made in this section.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graphical representation of portions of an example of acellular communication network.

FIG. 2 is a functional block diagram illustrating user equipment for acellular communication network.

FIG. 3 is a block diagram of portions of an embodiment of an RFcommunication device.

FIG. 4 is a block diagram of portions of an embodiment of an antennaaperture tuning circuit

FIG. 5 is a flow diagram of an embodiment of a method of antennaaperture tuning for an RF communication device.

DETAILED DESCRIPTION

The following description and the drawings sufficiently illustratespecific embodiments to enable those skilled in the art to practicethem. Other embodiments may incorporate structural, logical, electrical,process, and other changes. Portions and features of some embodimentsmay be included in, or substituted for, those of other embodiments.Embodiments set forth in the claims encompass all available equivalentsof those claims.

FIG. 1 illustrates an example of portions of a cellular communicationnetwork. In certain embodiments, the network is a Universal MobileTelecommunications System (UMTS) network. The network 100 can includemacro cells 105, 110 that service larger areas and can include smallercells 115, 120 that service smaller areas. FIG. 1 also illustrates userequipment (UE) 102 operating in the network. The UE 102 may be aportable wireless communication device, such as a personal digitalassistant (PDA), a laptop or portable computer with wirelesscommunication capability, a web tablet, a wireless telephone, asmartphone, a wireless headset, a pager, an instant messaging device, adigital camera, an access point, a television, a medical device (e.g., aheart rate monitor, a blood pressure monitor, etc.), or other devicethat may receive and/or transmit information wirelessly.

FIG. 2 illustrates a functional block diagram of UE for a cellularcommunication network. The UE may be suitable for use as any one or moreof the UEs 102 illustrated in FIG. 1. The UE may include physical layer(PHY) circuitry 203 for transmitting and receiving radio frequencyelectrical signals to and from one or more nodes of a radio accessnetwork using one or more antennas 201. The PHY circuitry 203 mayinclude circuitry for modulation/demodulation,upconversion/downconversion, filtering, amplification, etc. The UE mayalso include medium access control layer (MAC) circuitry 204 forcontrolling access to the wireless medium and to configure frames orpackets for communicating over the wireless medium. The UE may alsoinclude processing circuitry 206 and memory 208 arranged to configurethe various elements of the UE to perform the operations describedherein. The memory 208 may be used to store information for configuringthe processing circuitry 206 to perform the operations.

Although the UE is illustrated as having several separate functionalelements, one or more of the functional elements may be combined and maybe implemented by combinations of software-configured elements, such asprocessing elements including digital signal processors (DSPs), and/orother hardware elements. For example, some elements may comprise one ormore microprocessors, DSPs, application specific integrated circuits(ASICs), radio-frequency integrated circuits (RFICs), and combinationsof various hardware and logic circuitry for performing at least thefunctions described herein. In some embodiments, the functional elementsmay refer to one or more processes operating on one or more processingelements.

Embodiments may be implemented in one or a combination of hardware,firmware and software. Embodiments may also be implemented asinstructions stored on a computer-readable storage medium, which may beread and executed by at least one processor to perform the operationsdescribed herein. A computer-readable storage medium may include anynon-transitory mechanism for storing information in a form readable by amachine (e.g., a computer). For example, a computer-readable storagemedium may include read-only memory (ROM), random-access memory (RAM),magnetic disk storage media, optical storage media, flash-memorydevices, and other storage devices and media. In these embodiments, oneor more processors may be configured with the instructions to performthe operations described herein.

The one or more antennas 201 utilized by the UE 200 may comprise one ormore directional or omnidirectional antennas, including, for example,dipole antennas, monopole antennas, patch antennas, loop antennas,microstrip antennas or other types of antennas suitable for transmissionof radio frequency (RF) signals. In some embodiments, instead of two ormore antennas, a single antenna with multiple apertures may be used. Inthese embodiments, each aperture may be considered a separate antenna.In some multiple-input multiple-output (MIMO) embodiments, the antennasmay be effectively separated to take advantage of spatial diversity andthe different channel characteristics that may result between each ofantennas and the antennas of a transmitting station. In some MIMOembodiments, the antennas may be separated by up to 1/10 of a wavelengthor more.

FIG. 3 is a block diagram of portions of an embodiment of an RFcommunication device, such as UE for a cellular communication networkfor example. The device 300 includes an RF antenna circuit 301, anantenna aperture tuning circuit 310, and a processor circuit 306. Thedevice 300 also includes an antenna impedance measurement circuit thatincludes a power phase and amplitude detector 312. Also shown in FIG. 3are an impedance matching network 314 circuit, an RF transceiver 316, adirectional coupler 318, and an RF front end 320. The RF front end 320includes the RF filters used to reject an out of band signal whentransmitting and receiving RF signals. As shown in FIG. 3, the antennaaperture tuning circuit 310 can include or more RF switches 322 and caninclude one more tunable capacitors 324. The RF switches 322 can becoupled between a radiating element of the antenna 301 and a circuitcomponent, such as one or more of an inductor, capacitor, anotherradiating element of the antenna, and circuit ground for example. Theone or more tuning capacitors 324 can be coupled between a radiatingelement of the antenna 301 and either another radiating element of theantenna or a circuit ground.

FIG. 4 is a block diagram of portions of an embodiment of an antennaaperture tuning circuit 410. An antenna radiating element 401 isconnected to RF circuitry 405 at feed port 426 and by one or more tuningports 428 separate from the feed port 426. The RF circuitry 405 caninclude one or more of the RF circuitry blocks shown in FIG. 3. As shownin detail in FIG. 4, a tuning port 428 can include one or more of aninductor 430 coupled between the antenna radiating element 401 andcircuit ground by an RF switch 422, a capacitor 432 coupled between theantenna radiating element 401 and circuit ground by an RF switch 422, atleast a second antenna radiating element 434 coupled to the firstantenna radiating element 401 by an RF switch 422, and a circuit ground436 coupled to the antenna radiating element 401 by an RF switch 422.

In the embodiment shown, the tuning port includes a single-polefour-throw (SP4T) switch to connect the antenna radiating element 401 toone of the inductor 430, the capacitor 432, the second antenna radiatingelement 434, or the circuit ground 436. In certain embodiments, thetuning port 428 can include a different RF switch configuration toconnect one or a combination of the inductor, the capacitor, the secondradiating element and the circuit ground to the antenna radiatingelement 401. A processor 406 (e.g., a modem processor) is connected tothe RF switches. The antenna aperture tuning state is changed by theprocessor 406 changing the configuration of the RF switch or switches.

In some embodiments, the antenna aperture tuning state is set using atunable capacitor 424. In certain variations, the overall capacitance ofa tunable capacitor can be adjusted or tuned or by adding or removingunit sized capacitors to the tunable capacitor circuit. In othervariations, the overall capacitance could be tuned by changing thebiasing voltage to the dielectric material of the capacitor. A tuningport 428 can include one or both of: the antenna radiating element 401coupled to circuit ground by a tunable capacitor, and a second antennaradiating element coupled to the first antenna radiating element 401 bya tunable capacitor 424. The tunable capacitor could be replaced by acircuit consisting of a tunable capacitor connected in series with aninductor, connected in parallel with an inductor, or a combination ofserial and parallel connections with one or more inductors. Theprocessor 406 sets the antenna aperture tuning state by setting thecapacitance value of one or more tunable capacitors of the tuning portor ports. The tuning ports 428 may include both RF switches and tuningcapacitors. In some embodiments, the antenna aperture tuning circuit 410includes one or more tuning ports with a combination of componentsswitchable to the antenna radiating element by one or more RF switches422 and components electrically coupled to the antenna radiating element401 by one or more tunable capacitors 424. The processor 406 changes theantenna aperture tuning state by changing the capacitance value of oneor more tunable capacitors and activating/deactivating one or more RFswitches.

Returning to FIG. 3, the desired antenna aperture tuning state isdetermined according to antenna impedance measured by the antennaimpedance measurement circuit. As explained previously herein, theimpedance measurement circuit measures the complex reflectioncoefficient (N) at the reference plane. The impedance measurementcircuit may include the power phase and amplitude detector 312. Tomeasure antenna impedance, an RF signal is transmitted and the forwardsignal and the reverse signal are extracted using the directionalcoupler 318. The amplitudes of the forward and reverse signals (or theratio of the amplitudes of the forward and reverse signals), and therelative phase between the forward signal and reverse signal aremeasured. The complex reflection coefficient (Γ_(M)) may be determinedfrom the ratio of the amplitudes and the relative phase, and theimpedance at the reference plane is derived using the reflectioncoefficient. The impedance matching network 314 may be de-embedded toderive the raw impedance (Γ_(ANT)). The de-embedding could be analyticaland completed in real-time or runtime using a current circuit model (ortwo-port network mathematical model) of the impedance matching network.The de-embedding may be implicit in a lookup table based implementationwhere the effect of the impedance matching network 314 may bepredetermined and accounted for in the calculations.

In some embodiments, there are two separated signal paths to the powerphase and amplitude detector 312 for the forward and reverse signals.This allows the forward signal and the reverse signal to be extractedusing the directional coupler 318 and the forward reverse signals to bemeasured simultaneously. In other embodiments, the forward signal andthe reverse signal are extracted and measured sequentially. In someembodiments, the detection circuit is a differential detection circuitand the simultaneously extracted forward and reverse signals are fedinto the differential detection circuit to obtain a ratio of theamplitudes and the relative phase. In other embodiments, the amplitudedeterminations for the forward and reverse signal are performedseparately, and the ratio of the amplitudes is computed based on thedetected values. The phase detection is realized by correlating theextracted forward/reverse signal with a transmit reference signal (orI/Q signal). The detected phase of each of the forward signal and thereverse signal are compared to obtain the relative phase between theforward signal and the reverse signal. The amplitude and phase detectioncould be realized in a discrete circuit implemented using one or both ofanalog and digital circuits, or the detection could be integrated intothe RF transceiver utilizing the modem processor and completed in thedigital domain.

When the antenna raw impedance is obtained, it is determined if thecurrent antenna aperture tuning state is the desired or optimum statefor that impedance. If not, the processor circuit 306 changes theantenna aperture tuning state accordingly. This creates a closed loopcontrol of antenna aperture state based on antenna impedance. A lookuptable can be used to map the antenna aperture tuning states available topredetermined antenna impedances. The lookup table may be stored in amemory circuit 338 separate from, or integral to, the processor circuit306.

Table 1 below is an example of potions of a lookup table. In theleft-most column of Table 1 are antenna aperture tuning states thatcorrespond to the present tuning state of the device. Included for eachtuning state are multiple impedance ranges. For example, the impedanceranges for Tuning State 1 are Impedance Range 11, Impedance Range 12,Impedance Range 13 . . . Impedance Range 1N. The impedance ranges forTuning State 2 are Impedance Range 21, Impedance Range 22, ImpedanceRange 23 . . . Impedance Range 2N. The impedance ranges for Tuning StateN are Impedance Range N1, Impedance Range N2, Impedance Range N3 . . .Impedance Range NN.

TABLE 1 Aperture Tuning State Lookup Table Tuning Antenna Range Range 12Range 13 . . . Range 1N State 1 Impedance 11 Next Tuning 1 1 2 . . . 1State Tuning Antenna Range Range 22 Range 23 . . . Range 2N State 2Impedance 21 Next Tuning 2 1 2 . . . 2 State . . . . . . . . . . . . . .. . . . . . . Tuning Antenna Range Range N2 Range N3 . . . Range NNState N Impedance N1 Next Tuning . . . . . . . . . . . . . . . State

The lookup table maps the present Tuning State and the determinedantenna impedance to the desired tuning state. The lookup table mayindicate that the present tuning state is the best tuning, or the lookuptable may indicate that a different tuning state is the best tuningstate. For instance, if the present tuning state is Tuning State 1 andthe antenna impedance fall into impedance range 11, the lookup tableindicates that Tuning State 1 is the best antenna aperture tuning stateand the tuning state is not changed. If the present tuning state isTuning State 1 and the antenna impedance fall into impedance range 13,the lookup table indicates that Tuning State 2 is the best antennaaperture tuning state and the tuning state is changed to Tuning State 2.

The Tuning States of Table 1 may correspond to a configuration of RFswitches, a configuration of settings for one or more tunable capacitorsor tunable inductors, or any combination of RF switch configurations,capacitor configurations, and inductor configurations. The number ofantenna aperture tuning states that can be configured may exceed thenumber of aperture tuning states that are actually usable or desirable.A Tuning State of Table 1 may be mapped to a specific circuitconfiguration, such as by using a lookup table for example. The mappingmay be incorporated into a single lookup table that includes theimpedance mapping or a separate lookup table can be specifically usedfor the configuration mapping.

Table 2 below is an example of a lookup table to map Tuning States toactual circuit configurations. A Tuning State value is mapped to a rowthat includes a digital value that can be used to set the antennaaperture tuning state. For instance, assume the antenna aperture tuningstate is determined by the SP4T RF switch 422 in FIG. 4. The digitalvalue can be used to set the position of the RF switch 422 to couple theantenna radiating element 401 to one of the inductor 430, the capacitor432, the additional antenna radiating element 434, or the circuit ground436. The entries of Table 2 may be incorporated into Table 1 byexpanding the Tuning State rows to include the circuit configurationsettings. When a new Tuning is determined using the antenna impedancevalue, the digital for the circuit configuration may be loaded and usedto re-configure the antenna aperture tuning state.

TABLE 2 Tuning State 1 1 0 0 0 2 0 1 0 0 3 0 0 1 0 4 0 0 0 1

The example lookup tables are intended to be illustrative andnon-limiting. The antenna aperture tuning state may include moreconfigurable options resulting in more entries in the lookup table. Forinstance, each of the circuit components may be connectable to theantenna radiating element 401 by an individually controllable RF switch422. If the antenna aperture tuning circuit includes one or more tunablecapacitors 424 as described previously herein, the digital value of arow of the lookup table can be used to set the capacitance value of thetunable capacitor. In further embodiments, an equation or other meansmay be used to obtain the antenna aperture tuning state, but the lookuptable is likely sufficient and effective for this purpose.

Changing the antenna aperture tuning state can be viewed as a coarseadjustment of antenna performance or efficiency. Returning to FIG. 3,the impedance matching network 314 may be tunable to provide a fineadjustment for the antenna. A tunable impedance matching network mayinclude one or more of a tunable shunt capacitor coupled between anantenna radiating element and ground, a tunable capacitor seriallycoupled between radiating antenna elements, a tunable inductor coupledin serial or shunt configuration, and one or more RF switches coupled toa capacitor or inductor. The processor circuit 306 changes the impedanceof the impedance matching circuit by changing one or more of acapacitance value of an tunable capacitor, an inductance value of atunable inductor, and a state of one or more RF switches of theimpedance matching circuit 314.

Once the antenna aperture tuning state is configured by the processorcircuit 306, the processor circuit 306 may adjust the impedance matchingnetwork 314 to optimize a figure of merit of the antenna, such as bytuning the impedance matching circuit to increase the transducer gain ofthe impedance matching circuit 314. Thus, the tuning by the processorcircuit 306 can provide closed loop coarse tuning and closed loop finetuning of the antenna circuit. The processor circuit 306 may continue tomake the fine adjustments and continue to monitor the antenna rawimpedance. When the antenna raw impedance changes to a new impedancevalue or a new impedance range that changes the entry in the lookuptable, the processor circuit 306 loads and configures the new antennaaperture tuning state.

FIG. 5 is a flow diagram of an embodiment of a method 500 of antennaaperture tuning for an RF communication device. At 505, an initial orcurrent antenna aperture tuning state is set according to one or moreparameters of the RF communication network. Some examples of the networkparameters include a radio access technology (RAT) of the RFcommunication network, a channel frequency band of the RF communicationnetwork, and bandwidth of the RF communication network. The antennaaperture tuning state can be set by configuring tunable capacitors,tunable inductors and RF switches as described previously.

The next step is to determine the antenna impedance and determinewhether the current antenna aperture tuning state is the best one suitedfor the measured impedance. A processor may recurrently initiate themeasurement of antenna impedance according to a specified schedule. Insome embodiments, the measurement of antenna impedance may be initiatedwhen a parameter of the RF communication network changes.

At 510, it is determined whether a timer expired to initiate the nextantenna impedance measurement. The antenna impedance can be measuredusing a forward signal and a reverse signal of a transmit signal, suchas described previously. At 515, it is determined whether the power ofthe transmit signal (P_(TX)) is strong enough for an accurate impedancemeasurement.

At 520, if the transmit power is less than a specified threshold power,the current aperture tuning state is maintained at 525 and the processwaits until it is time for another antenna impedance measurement. If thetransmit power satisfies the specified threshold power, at 530 theantenna impedance is derived, such as by determining the reflectioncoefficient from forward and reverse signals as described previously andderiving the antenna impedance using the reflection coefficient.

At 535, the best antenna aperture tuning state is determined accordingto the measured antenna impedance, such as by using a lookup table. At540, if the best antenna aperture tuning state is the same as thecurrent antenna aperture tuning state according to the measured antennaimpedance, the process returns to 510 to wait for the next antennaimpedance measurement to be initiated. Which aperture is best may dependon the current use case of the device, such as whether the device isbeing used in free space (FS), beside the head (BH) of the user, besidethe head and hand left side (BHHL), beside the head and hand right side(BHHR). Other reasons can cause the overall antenna radiating efficiencyto become less than the efficient of another antenna aperture tuningstate. If the best antenna aperture tuning state is different from thecurrent antenna aperture tuning state, at 545 the current antennaaperture tuning state is changed to the determined best state. Theprocess returns to 510 to wait for the next antenna impedancemeasurement to be initiated.

In some embodiments, further fine tuning is performed when the antennaaperture tuning state is changed. The RF communication device mayinclude an impedance matching circuit that is tunable, such as byadjusting a tunable capacitor of the impedance matching circuit forexample. Further aperture tuning may be performed with coarse aperturestate tuning. The coarse aperture tuning states are realized by RFswitches, while fine aperture tuning is realized using tunablecapacitors or tunable inductors with fine tuning capability. A lookuptable may be created for the coarse aperture tuning states, and the fineaperture tuning is realized by monitoring the reflection coefficient andby a comparison with a predetermined value for a desired figure of meritparameter. The figure of merit parameter can be used as feedback foradjustment of the capacitance value of the tunable capacitor by theprocessor.

In some embodiments, only fine tuning is included under closed loopcontrol by a processor. An initial antenna aperture tuning state may beselected (e.g., by a lookup table) from a few coarse tuning states basedon one or more operating parameters such as RAT, band, frequency and usecase. After the initial antenna aperture tuning state is set, theprocessor fine tunes one or more adjustable circuit components of theimpedance matching circuit to optimize the figure of merit parameter. Insome embodiments, the fine tuning is realized by monitoring a reflectioncoefficient and adjusting the one or more circuit components to adjustthe reflection coefficient toward a predetermined value.

The several examples described provide solutions to optimize antennaefficiency for all frequency bands under changing conditions in whichthe RF device is used. The RF device accomplishes this by reconfiguringthe antenna aperture in real time.

Additional Description and Examples

Example 1 includes subject matter (such as an apparatus) comprising aradio frequency (RF) antenna circuit; an antenna aperture tuningcircuit; an antenna impedance measurement circuit; and a processorcircuit electrically coupled to the tunable antenna aperture circuit andthe impedance measurement circuit, wherein the processor circuit isconfigured to: set the antenna aperture tuning circuit to an antennaaperture tuning state according to one or more parameters of an RFcommunication network; initiate an antenna impedance measurement toobtain an antenna impedance; and adjust the antenna aperture tuningstate as a function of the antenna impedance.

In Example 2, the subject matter of Example 1 optionally includes anantenna aperture tuning circuit that includes one or more of: aninductor coupled to the RF antenna circuit by an RF switch, a capacitorcoupled to the RF antenna circuit by an RF switch, at least a firstantenna radiating element coupled to a second antenna radiating elementby an RF switch, an antenna radiating element coupled to a circuitground by an RF switch; and wherein the processor circuit is configuredto set the antenna aperture tuning state by configuring one or more RFswitches of the antenna aperture tuning circuit.

In Example 3, the subject matter of one or both of Examples 1 and 2optionally includes an antenna aperture tuning circuit that includes oneor more of: at least a first antenna radiating element coupled to asecond antenna radiating element by a tunable capacitor; and an antennaradiating element coupled to a circuit ground by a tunable capacitor;and wherein the processor circuit is configured to set the antennaaperture tuning state by setting the capacitance value of one or moretunable capacitors.

In Example 4, the subject matter of one or any combination of Examples1-3 optionally includes an impedance matching circuit electricallycoupled to the RF antenna circuit, wherein the processor circuit isoptionally configured to change impedance of the impedance matchingcircuit to change transducer gain of the RF antenna circuit when theantenna aperture tuning state is set to the antenna aperture tuningstate indicated by the antenna impedance.

In Example 5, the subject matter of one or any combination of Examples1-4 optionally includes a memory circuit configured to store a lookuptable that includes antenna aperture tuning states indexed according toantenna impedance, wherein the processor circuit is configured to setthe antenna aperture tuning state using the lookup table.

In Example 6, the subject matter of one or any combination of Examples1-5 optionally includes an adjustable capacitor electrically coupledbetween one of a radiating element and circuit ground, or a firstradiating element and a second radiating element, wherein the processorcircuit is configured to set the antenna aperture tuning state bychanging a capacitance value of the adjustable capacitor.

In Example 7, the subject matter of one or any combination of Examples1-6 optionally includes a transmit power measurement circuit configuredto determine a measure of transmit power, and wherein the processorcircuit is configured to initiate a measurement of transmit power, andinitiate the antenna impedance measurement conditional upon themeasurement of transmit power satisfying a specified measurementtransmit power threshold.

In Example 8, the subject matter of one or any combination of Examples1-7 optionally includes an antenna impedance measurement circuitconfigured to determine magnitude and phase of a forward signal and areverse signal of a transmit signal, and wherein the processor circuitis configured to determine the antenna impedance measurement using adifference in phase between the forward signal and the reverse signal,and a ratio including the magnitudes of the forward signal and thereverse signals.

In Example 9, the subject matter of one or any combination of Examples1-8 optionally includes a processor circuit configured to recurrentlyinitiate the measurement of antenna impedance according to a specifiedschedule, and change the antenna aperture tuning state according to thedetermined antenna impedance.

In Example 10, the subject matter of one or any combination of Examples1-9 optionally includes a processor circuit configured to set theaperture tuning circuit to an antenna aperture tuning state and initiatethe measurement of antenna impedance when detecting a change in the oneor more parameters of the RF communication network.

In Example 11, the subject matter of one or any combination of Examples1-10 optionally includes a processor circuit configured to set theantenna aperture tuning circuit to an antenna aperture tuning stateaccording to one or more parameters that include one or more of a radioaccess technology (RAT) of the RF communication network, a channel ofthe RF communication network, and bandwidth of the RF communicationnetwork.

Example 12 includes subject matter (such as a computer readable storagemedium including instructions that when performed by processingcircuitry of an RF communication device, cause the RF communicationdevice to perform specified operations), or can optionally be combinedwith the subject matter of one or any combination of Examples 1-11 toinclude such subject matter, comprising setting an antenna aperturetuning state according to one or more parameters of the RF communicationnetwork; determining antenna impedance; and changing the antennaaperture tuning state according to the determined antenna impedance.

In Example 13, the subject matter of Example 12 optionally includes oneor more of: changing an RF coupling state of a first antenna radiatingelement to a second radiating element, changing an RF coupling state ofan antenna radiating element to ground, changing an RF coupling state ofan antenna radiating element to an inductor of an antenna circuit of theRF circuitry, changing an RF coupling state of an antenna radiatingelement to a capacitor of the antenna circuit, and changing an RFcoupling location of a ground leg of an RF antenna circuit of the RFcircuitry.

In Example 14, the subject matter of one or both of Examples 12 and 13optionally include tuning an impedance matching circuit to changetransducer gain of an RF antenna circuit of the RF circuitry in additionto changing the antenna aperture tuning state.

In Example 15, the subject matter of one or any combination of Examples12-14 optionally includes identifying an antenna aperture tuning stateusing a lookup table that includes specified antenna aperture tuningstates indexed according to antenna impedance, and setting the antennaaperture tuning state to a specified antenna aperture tuning stateidentified using the lookup table.

In Example 16 the subject matter of one or any combination of Examples12-15 optionally includes setting the antenna aperture tuning state byadjusting a capacitance value of a capacitor, wherein the capacitor iselectrically coupled between one of a radiating element and circuitground, or a first radiating element and a second radiating element.

In Example 17, the subject matter of one or any combination of Examples12-16 optionally includes determining the magnitude of transmit power,wherein the determining antenna impedance is conditional upon thedetermined magnitude of transmit power satisfying a specified thresholdmagnitude value.

In Example 18, the subject matter of one or any combination of Examples12-17 optionally include determining magnitude and phase of a transmitsignal from a forward direction and a reverse direction, and determiningthe antenna impedance using a difference in phase between the transmitsignal in the forward direction and the reverse direction, and a ratioincluding the magnitudes of the transmit signal in the forward directionand the reverse direction.

Example 19, can include subject matter (such as a method of operating anambulatory medical device, a means for performing acts, or amachine-readable medium including instructions that, when performed bythe machine, cause the machine to perform acts), or can optionally becombined with the subject matter of one or any combination of Examples1-18 to include such subject matter, comprising setting an antennaaperture tuning state according to parameters of the RF communicationnetwork; determining antenna impedance; determining a figure of meritparameter for the antenna aperture tuning state using the antennaimpedance; and changing the antenna aperture tuning state according tothe figure of merit parameter.

In Example 20, the subject matter of Example 19 optionally includes acomputer readable storage medium including instructions to causeprocessing circuitry of the RF communication device to select an antennaaperture tuning state using a lookup table that includes antennaaperture tuning states indexed according to antenna impedance, and setthe antenna aperture tuning state to the selected antenna aperturetuning state.

Example 21 can include, or can optionally be combined with any portionor combination of any portions of any one or more of Examples 1-20 toinclude, subject matter that can include means for performing any one ormore of the functions of Examples 1-20, or a machine-readable mediumincluding instructions that, when performed by a machine, cause themachine to perform any one or more of the functions of Examples 1-20.

These non-limiting examples can be combined in any permutation orcombination.

The above detailed description includes references to the accompanyingdrawings, which form a part of the detailed description. The drawingsshow, by way of illustration, specific embodiments in which theinvention can be practiced. These embodiments are also referred toherein as “examples.” All publications, patents, and patent documentsreferred to in this document are incorporated by reference herein intheir entirety, as though individually incorporated by reference. In theevent of inconsistent usages between this document and those documentsso incorporated by reference, the usage in the incorporated reference(s)should be considered supplementary to that of this document; forirreconcilable inconsistencies, the usage in this document controls.

Method examples described herein can be machine or computer-implementedat least in part. Some examples can include a computer-readable storagemedium or machine-readable storage medium encoded with instructionsoperable to configure an electronic device to perform methods asdescribed in the above examples. An implementation of such methods caninclude code, such as microcode, assembly language code, a higher-levellanguage code, or the like. Such code can include computer readableinstructions for performing various methods. The code may form portionsof computer program products. The code can be tangibly stored on one ormore volatile, non-transitory, or non-volatile tangiblecomputer-readable media, such as during execution or at other times.Examples of these tangible computer-readable storage media can include,but are not limited to, hard disks, removable magnetic disks, removableoptical disks (e.g., compact disks and digital video disks), magneticcassettes, memory cards or sticks, random access memories (RAMs), readonly memories (ROMs), and the like.

The Abstract is provided to allow the reader to ascertain the nature andgist of the technical disclosure. It is submitted with the understandingthat it will not be used to limit or interpret the scope or meaning ofthe claims. The following claims are hereby incorporated into thedetailed description, with each claim standing on its own as a separateembodiment. Also, in the following claims, the terms “including” and“comprising” are open-ended, that is, a system, device, article, orprocess that includes elements in addition to those listed after such aterm in a claim are still deemed to fall within the scope of that claim.Moreover, in the following claims, the terms “first,” “second,” and“third,” etc. are used merely as labels, and are not intended to imposenumerical requirements on their objects.

What is claimed is:
 1. An apparatus comprising: a radio frequency (RF)antenna circuit; an antenna aperture tuning circuit; an antennaimpedance measurement circuit; and a processor circuit electricallycoupled to the tunable antenna aperture circuit and the impedancemeasurement circuit, wherein the processor circuit is configured to: setthe antenna aperture tuning circuit to an antenna aperture tuning stateaccording to one or more parameters of an RF communication network;initiate an antenna impedance measurement to obtain an antennaimpedance; and adjust the antenna aperture tuning state as a function ofthe antenna impedance.
 2. The apparatus of claim 1, wherein the antennaaperture tuning circuit includes one or more of: an inductor coupled tothe RF antenna circuit by an RF switch, a capacitor coupled to the RFantenna circuit by an RF switch, at least a first antenna radiatingelement coupled to a second antenna radiating element by an RF switch,an antenna radiating element coupled to a circuit ground by an RFswitch; and wherein the processor circuit is configured to set theantenna aperture tuning state by configuring one or more RF switches ofthe antenna aperture tuning circuit.
 3. The apparatus of claim 1,wherein the antenna aperture tuning circuit includes one or more of: atleast a first antenna radiating element coupled to a second antennaradiating element by a tunable capacitor; and an antenna radiatingelement coupled to a circuit ground by a tunable capacitor; and whereinthe processor circuit is configured to set the antenna aperture tuningstate by setting the capacitance value of one or more tunablecapacitors.
 4. The apparatus of claim 1, including an impedance matchingcircuit electrically coupled to the RF antenna circuit, wherein theprocessor circuit is configured to change impedance of the impedancematching circuit to change transducer gain of the RF antenna circuitwhen the antenna aperture tuning state is set to the antenna aperturetuning state indicated by the antenna impedance.
 5. The apparatus ofclaim 1, including a memory circuit configured to store a lookup tablethat includes antenna aperture tuning states indexed according toantenna impedance, wherein the processor circuit is configured to setthe antenna aperture tuning state using the lookup table.
 6. Theapparatus of claim 1, including an adjustable capacitor electricallycoupled between one of a radiating element and circuit ground, or afirst radiating element and a second radiating element, wherein theprocessor circuit is configured to set the antenna aperture tuning stateby changing a capacitance value of the adjustable capacitor.
 7. Theapparatus of claim 1, including a transmit power measurement circuitconfigured to determine a measure of transmit power, and wherein theprocessor circuit is configured to initiate a measurement of transmitpower, and initiate the antenna impedance measurement conditional uponthe measurement of transmit power satisfying a specified measurementtransmit power threshold.
 8. The apparatus of claim 1, wherein theantenna impedance measurement circuit is configured to determinemagnitude and phase of a forward signal and a reverse signal of atransmit signal, and wherein the processor circuit is configured todetermine the antenna impedance measurement using a difference in phasebetween the forward signal and the reverse signal, and a ratio includingthe magnitudes of the forward signal and the reverse signals.
 9. Theapparatus of claim 1, wherein the processor circuit is configured torecurrently initiate the measurement of antenna impedance according to aspecified schedule, and change the antenna aperture tuning stateaccording to the determined antenna impedance.
 10. The apparatus ofclaim 1, wherein the processor circuit is configured to set the aperturetuning circuit to an antenna aperture tuning state and initiate themeasurement of antenna impedance when detecting a change in the one ormore parameters of the RF communication network.
 11. The apparatus ofclaim 1, wherein the one or more parameters of the RF communicationnetwork include one or more of a radio access technology (RAT) of the RFcommunication network, a channel of the RF communication network, andbandwidth of the RF communication network.
 12. A computer readablestorage medium including instructions, that when performed by processingcircuitry of an RF communication device, cause the RF communicationdevice to perform acts comprising: setting an antenna aperture tuningstate according to one or more parameters of the RF communicationnetwork; determining antenna impedance; and changing the antennaaperture tuning state according to the determined antenna impedance. 13.The computer readable storage medium of claim 12, including instructionsthat cause the RF communication device to perform acts comprisingchanging the antenna aperture tuning state by one or more of: changingan RF coupling state of a first antenna radiating element to a secondradiating element, changing an RF coupling state of an antenna radiatingelement to ground, changing an RF coupling state of an antenna radiatingelement to an inductor of an antenna circuit of the RF circuitry,changing an RF coupling state of an antenna radiating element to acapacitor of the antenna circuit, and changing an RF coupling locationof a ground leg of an RF antenna circuit of the RF circuitry.
 14. Thecomputer readable storage medium of claim 12, including instructionsthat cause the RF communication device to perform acts comprising tuningan impedance matching circuit to change transducer gain of an RF antennacircuit of the RF circuitry in addition to changing the antenna aperturetuning state.
 15. The computer readable storage medium of claim 12,including instructions that cause the RF communication device to performacts comprising changing the antenna aperture tuning state byidentifying an antenna aperture tuning state using a lookup table thatincludes specified antenna aperture tuning states indexed according toantenna impedance, and setting the antenna aperture tuning state to aspecified antenna aperture tuning state identified using the lookuptable.
 16. The computer readable storage medium of claim 12, includinginstructions that cause the RF communication device to perform actscomprising setting the antenna aperture tuning state by adjusting acapacitance value of a capacitor, wherein the capacitor is electricallycoupled between one of a radiating element and circuit ground, or afirst radiating element and a second radiating element.
 17. The computerreadable storage medium of claim 12, including instructions that causethe RF communication device to perform acts comprising determiningmagnitude of transmit power, wherein the determining antenna impedanceis conditional upon the determined magnitude of transmit powersatisfying a specified threshold magnitude value.
 18. The computerreadable storage medium of claim 12, including instructions that causethe RF communication device to perform acts comprising determiningmagnitude and phase of a transmit signal from a forward direction and areverse direction, and determining the antenna impedance using adifference in phase between the transmit signal in the forward directionand the reverse direction, and a ratio including the magnitudes of thetransmit signal in the forward direction and the reverse direction. 19.A method of operating radio frequency (RF) circuitry to communicate viaan RF communication network, the method comprising: setting an antennaaperture tuning state according to parameters of the RF communicationnetwork; determining antenna impedance; determining a figure of meritparameter for the antenna aperture tuning state using the antennaimpedance; and changing the antenna aperture tuning state according tothe figure of merit parameter.
 20. The method of claim 19, includingselecting an antenna aperture tuning state using a lookup table thatincludes antenna aperture tuning states indexed according to antennaimpedance, and setting the antenna aperture tuning state to the selectedantenna aperture tuning state.